eHam Forums => Amplifiers => Topic started by: K5MF on August 22, 2012, 04:37:43 PM

Title: 2m Amps
Post by: K5MF on August 22, 2012, 04:37:43 PM
Here or VHF forum, I am not sure. 

My school was just awarded an ARISS contact.  We are now tasked with putting together the 2 redundant stations.  Requirements require 100+ watts.  We have an FT857 and FT897 as the contact radios so we are limited to 50 watts barefoot.  I thought about hooking the antenna connectors in series to get 100 watts but then thought better of that idea (not really).  So it looks like we are in the market for a couple of 2 meter 100+ watt amplifiers.  From what I can tell, my there are only a couple of manufacturers of 2m amps - Mirage and Tokyo.  Tokyo seems to only make one 2 meter amp right now and it is 350 watts and quite pricey.  Therefore, my conclusion is that mirage amps are the only realistic solution to the issue.  Some of the product reviews for Mirage are not too good, but I am hoping the problems are with the older units and the newer units may be of at least high enough quality to use on the very temporary basis that it will - an occasional Sat or ISS contact.

Is my thinking correct?  Or please fill me in on what I haven't yet discovered.



Title: RE: 2m Amps
Post by: N3JBH on August 22, 2012, 07:10:17 PM
there is also there pretty well known and good.

Title: RE: 2m Amps
Post by: VR2AX on August 22, 2012, 07:11:43 PM

THP make a 100/140 watt amp, also a 200 watt amp, for 2m. I have owned the former and it is well made, also quite a few Hong Kong hams use or used the (now getting on a bit) 200 watt amp (which requires 50 watts drive):

I believe they have to be ordered direct from THP because these particular models are not FCC approved.



Title: RE: 2m Amps
Post by: N5VTU on August 23, 2012, 10:02:26 AM
Congrats on your ARISS contact.  What school do you teach at and when is your contact scheduled?  I'm just north of Houston and would be happy to loan you a 2m amp for your contact.

Contact me via email - n5vtu at arrl dot net if you're interested.


Title: RE: 2m Amps
Post by: N6AJR on August 23, 2012, 11:56:41 AM
I use a mirage 2 m amp, 10 w in and 160 w out, and get it used  for about 150 bucks.  check and see if someone locally can loan you an amp and a power supply large enough to run the amp.  good luck and enjoy.

Title: RE: 2m Amps
Post by: K5MF on August 24, 2012, 03:22:33 AM
Thanks for the input!  Good information.  All things considered, I think the mirage amps are reasonably priced and hopefully will meet our limited use needs.  I did consider the non certified amps including  RL Italy but would like to encourage my kiddos to keep within the letter of the rules.  I don't see us using these amps on a daily basis but rather just for a few on-air tests and the contact.  Following our contact I would like to become an ARISS technical mentor so perhaps I can use the amps to help out other schools with their contacts in the future.  If anyone feels really strongly that I should not consider Mirage, please contact me offline at maxwellt at aol dot com. 

FYI, our school club KF5NZD plans to operate in the School Club Roundup in October so please listen for us on the air then if not sooner.  We are very excited to have been offered this contact and we appreciate NASA, ARRL, AMSAT, and the entire ARISS volunteer team for making this possible.  We are located in the far west Houston suburbs in a Katy TX zip code.  We receive support from the Katy Amateur Radio Society, (KARS) and appreciate all they do for the school and our kids.

If anyone would like to make a small personal contribution to our club or if you work for a company that would like to help sponsor the club or this ARISS event, please contact me.  Every donation no matter how small is greatly appreciated and will be put to good use teaching our kiddos technology.



Title: RE: 2m Amps
Post by: KB1GTX on August 24, 2012, 06:53:18 AM
Why not put the cash into a nice big yagi antenna?,,

Title: RE: 2m Amps
Post by: K5MF on August 24, 2012, 08:57:58 PM
Why not put the cash into a nice big yagi antenna?,,

Well a couple of reasons.  First, we are going to have the kiddos build a circular polarized yagi.  We are leaning towards the KG4JJH 6 element design available on the internet.  Second, ARISS requires that ISS contacts must be supported with two complete and independent radio systems, each capable of 100+ watts output.  That is not EFP but 100+ watts into the cable.  The reasons are pretty clear; sometimes school setups require long cable runs so a great deal of attenuation occurs and they want to maximize the probability of a successful contact.  The ISS gets hammered with lot of QRM every time it passes over, so they want to make sure the astronauts get the school signal.  Regardless of the antenna gain, they still set the minimum power to 100+ watts.  Since they are the only kid in town with a space station to talk to, we must play by their rules.  I have no problems with the requirements.  There have only been about 750 ISS school contacts since the beginning of the program in 2000 so if I can get a slot I'll follow the rules.



Title: RE: 2m Amps
Post by: KM3F on August 25, 2012, 12:50:16 PM
I hear your requirements.
Many SS amplifiers will make 160 watts rated power from about 22 amps at various input levels depending on what you have to drive them with.
They are mostly 10, 30 and 50 watt input drive levels available.
For your use I would equip any of them with a computer type cooling fan such as the ROCKFISH RF 120 located right center of the cooling fins just layng on the top, no housing, just some hold down of a sort.
Next , I have no idea of the length of you transmission lines so an example to see.
If you use LMR 400, the loss per 100 feet is about 1.5 DB per 100' at 150 mhz.
So if your line is 200 feet at 3db you lose half the power at 160 watts or about 80 watts into the antenna.
Now figure any antenna gain to find the ERP.
If you feel this is not enough then you need  300 watt level amplifers to cover for a narrow margin.
Those amplifiers require big power supplies.
Add to all this an AZ-EL rotator for tracking and a computer program to see where you need to track.
Cushcraft makes an antenna that can be set up for circular as well, unless you want the kids to do the building.
If you can get 7/8" Heliax transmission line donated by a com tower company, the loss goes way down for the length you might need but it needs N type connector that are not cheap.
Good luck.

Title: RE: 2m Amps
Post by: KB1GTX on August 25, 2012, 05:22:44 PM
But the thing is we at timberlane hs, can contact the iss on a 50 radio and just omni antennas, all we need to do is pick a time when it's kind of lower on the horizon.

Title: RE: 2m Amps
Post by: KG4RUL on August 25, 2012, 09:13:38 PM
I made a rock solid ISS contact during the 2011 Jamboree-On-The-Air (JOTA) using 50W and a dual-band vertical with 6dB gain.  And, wouldn't you know it, not a single Scout near the radio! The pass was low on the horizon and I have the confirming QSL card for the contact.  So, power is nice but, not absolutely necessary.  However, I do understand the desire for higher transmit power to improve the odds of a successful contact.

Title: RE: 2m Amps
Post by: K5MF on August 26, 2012, 06:53:09 PM
Thanks for the input.  We will use LMR400.  The run will be about 130' so the losses shouldn't be too bad.  Yes Heliax would be much better, but these are not permanent installations and Heliax would be very difficult to work with in this situation.  I went to the TI2 institute (Great Opportunity) and DARA presented all of the teachers with a Yaesu 5500 rotator, an FT817ND radio, NOVA Software, and an Arrow dual band antenna.  Really nice folks!  We made plenty of Satellite contacts with that setup and 5 watts.  For this contact we will use an FT897 with an FT857 as backup.  Requirements require a circularly polarized Yagi.

Two years ago I was driving down the east coast just south of Norfolk. I had my FT857 scanning on 2 meters into a mag-mount Larsen dual band vertical.  The radio stopped scanning and I heard as clear as day, "You are 59 on the ISS, 73."  I tried to contact him but couldn't bust the pileup.  If I had had 160 watts and a direction Yagi, it would have been no problems at all.

So yes it is possible to work the ISS with low power and a simple antenna.  The only problem is NASA and ARISS are not going to let you play the game unless you have 2 stations both capable of producing 100+ watts.  Yes they are being overly conservative, IMO, but you have to remember, they are dealing with all kinds of locations where it might be necessary to run 400+ feet of cable to get in a school building.  They are trying to cover worst case scenarios and I don't blame them.  This is not a random contact during play time.  These are scheduled mission events and major PR events for everyone involved.  They need to have a very high success rate.  From my standpoint, if we are going to stop school instruction and put 1300 students plus parents, VIPs including congressional representatives, and media news teams in front of us, it better dang work and I better be able to get through.

So I don't mind meeting the standards, I am confident a 160w amp will work just fine.  I am just trying to figure out what my options are on the limited budget that I have.

Thanks for the input.  We are really excited.

Title: RE: 2m Amps
Post by: VE1IDX on August 27, 2012, 07:23:42 AM
Rather than just making a blanket requirement of 100 watts transmitter power regardless of the antenna type to account for losses, wouldn't it make much more sense to state an ERP requirement? Stations would be able to meet those requirements with either antenna gain or sheer RF power.

Title: RE: 2m Amps
Post by: K5MF on August 28, 2012, 07:47:11 PM
Rather than just making a blanket requirement of 100 watts transmitter power regardless of the antenna type to account for losses, wouldn't it make much more sense to state an ERP requirement? Stations would be able to meet those requirements with either antenna gain or sheer RF power.

Remember, I am not a part of the ARISS team so I am not in on the meetings so I do not know if there is an official answer to this question.  I do know that these issues have been discussed, as have others.  I cannot definitively tell you why the rules are as they are.  I can only speculate.

A technical mentor will be assigned to our school and I hope to be in contact with him in the near future.  I'll ask him this very question and see if he knows.

Title: RE: 2m Amps
Post by: KB1GTX on August 30, 2012, 06:55:41 AM